Resistance conductor



Dec. 1947- w. ALLEVA El AL 2,432,268

RESIS'1ANCE CONDUCTOR Filed Dec. 14. 1944 INVENTORS WILLIAM ALLEVA .F g 2 Y v HERBERI BLACKBURN ATTORNEY Patented Dec. 9, 1947 UNITED STATES PATENT OFFICE RESISTANCE CONDUCTOR Application December 14, 1944, Serial No. 568,192

1 Claim. 1

Our present invention relates to resistors of the type wound on a ceramic tube and having metallic ferrule terminals. More specifically, our invention relatos to the means for mounting the metallic ferrules on the ends of a ceramic tube in such manner that they Will not be dislodged duringor after any firing or other heat treating processes to form a vitreous coating on the outside of the wound resistance wire.

Our invention contemplates metallic ierrule cups having a series of indentations or dimples on the periphery thereof whereby the cups may be forced over the ends of the ceramic resistor form or tube so that the tension of the indentations or dimples pressing against the outside of the ceramic tube is sufficient to keep the ferrule cup tightly in place. These indentations or dimples are sufficient to keep the ferru1e from loosening while the whole resistor unit is subject to the high temperatures required for firing or b-aking of a vitreous enamel insulating coating thereover.

For many years after the advent of the ferrule type resistor, it was common practice to aflix the ferrules only after the firing or heat treating process had occurred; this was accomplished by the use of metal slugs cemented inside the ceramic form, or by the use of a screw bolt. Any attempt to fasten the ferrules to the ceramic tube before the firing process resulted in failure, owing to the fact that the difference in expansion between the ceramic material and the metallic ferrule material was so great that the ferrules invariab1y loosened under the customary high firing temperatures.

One departure from the forego-ing methods was that of utilizng a ierrule of metallic material having a relatively low coefficient of expansion, together with a shim or insert of special design made of a soft metal With a, higher coefiicient of expansion than the ferrule. This shim or insert was placed inside the ferrule and the whole was forced over the outside of the ceramic tube Which resulted in the shim or insert taking up the excess space between the inside wall of the ferrule and the outside wall of the tube. Thus on a rise in temperature, the shim expanded more than the ferrule cup and thereby kept the ferrule tight on the ceramic material which was negligible expansion.

Our invention contemplates a further and novel step which dispenses entirely with any shim or insert and thus decreases the number of operations necessary in the manufacture of the resistor while, nevertheless, retaining all the advantages of a tight ferrule on the ceramic tube during al] of the operations. Our invention also makes possible the formation of transverse hole through the entire length of the resistor open to the free air to aid in heat dissipation.

A primary object of our invention, therefore, is the provision of novel simplified means for secur ing a metallic ferrule cup to a ceramic resistor form in such manner that the ferrule will not be dislodged during baking, firing, or other heat treating processes.

Another object of our invention is the formation of the ferrule so that the securing means are integral with the ferrule and need not be separately handled in any way.

Still another object is the formation of the integral securing means for the ferrule in a simplified easily produced, easily handled manner.

Still a further object of our invention is the formation of tensiomng means integral With the metallic ferrule cup in order at al] times to maintain the mounting of the metallic ferrule cup on the resistor form irrespective of the temperature to which the said resistor form is subjected,

A specific object of our invention is,the formation of indentations or dimples at spaced portions of the eriphery of the ferru1e in order to enable the same to grip the sides of the ceramic resistor form at all times irrespective of the temperature to which the entire unit is subjected.

Another object is the provision of simple wire connecting means for the ferrule.

These and many other objects of our invention will become apparent from the following description and drawings in which:

Figure 1 is a view in perspective of a hollow ceramic resistor form with the metallic ferrule cup mountedthereon.

Figure 2 is a cross-sectional view taken on line 22 of Figure 5.

Figures 3 and 4 are side views of metallic ferrule cups showing slightly modified indentations or tensioning means thereon.

Figure 5 is a view in perspective showing novel connector for the ferrule.

Referring now to Figure 1, we have here shown a hollow tubular resistor form IE! of ceramic material having the through opening l I. Metallic ferrule cups [5, l5 at each end each have opening l6 which registers with the opening l l of the tube IO when the ferrules l5 are mounted over the end of the tube IB. Each ferrule 15 has an annular end flange |8 which defines the opening IG and bears against the end [9 of the tube thus limiting and determining the position of the metallic ferrule cup with respect to the tube la. Each ferrule 15 also has a cylindrical side wall 20, the inside diameter of which is very slightly larger than the outside diameter of the tube IO. The cylindrical wall 20 of each of the ferruies l5 has a fiared annular flange 2|, the slight fiare 22 of which facilitates the pushing of the metallic ferrule cup I5 over the end of the tube IO. The fiange 2| has a re-entrant lip 25 in order to provide a finished appearance and construction.

The entire fiange 2| with its reentrant lip 25 is provided with a pair of spaced cuts 21, 23, as

shown in Figure 1, which provide a ready means V of securement for the resistance wire. T-hus, when the resistance is wound on the form l, one end of the resistance is caught at the cuts or mounting means 21, 28 by being secured thereto in any suitable manner as, for instance, by being twisted around the material 29 between the cuts or openings 21, 28; the wire is then wound on the form lil until it reaches the opposite ferrule and the opposite end of the resistor wire is secured thereto in the same manner.

The cylindrical wall 20 or periphery of the ferrule 15 is provided With a series of part spherical indentations 3D, 30 (Figure 1). The circle defined by the interior surfaces of these indentations is essentially of less circumference than the outside Circumference of the ceramio tube !'3. However, the metallic ferrule cup (which is preferably made of Mnel metal) is sufciently elastic so that the said cup may be forced over the end of tube 0, and be slightly expanded by reason of the pressure of the indentations 30 against the Outer surface of the tube lo.

We have found that after the resistance wire has been wound on the resistor form H] and a suitable vitreous enamel coating applied thereover, and the entire unit subjected to baking, firing or other heat 'treating processes, that the metallic ferrule cup 'l5 nevertheless maintains its predetermined position with respect to the ceramic tube IO, has no movement Whatever with respect thereto, does not become loosened with respect thereto at any time during the heat treating process or thereafter, and at al] times is securely integrated with the ceraini'c tube ll).

Since the material of the metallic ferrule cup 5 is elastically distorted by reason of the pressure of the indentations against the sides of the ceramic tube IO when the metallic ferrule cup l is forced thereon, any expansion of the metallic ferrule cup during the heat treating process is coinpensated for by the tendenoy of the material of the metallic ferrule cup l5 to return to its original undistorted position. Consequently, the indentations 30 need only be deep enough to compensate for the expansion of the material of the -metallic ferrule cup l5. They may be slightly deeper in order to ensure a perfict grip at all times. The essential element is that the indentations 33 be sufiiciently deep so that -irrespective of the amount of expansion which may normally be expected of the material of the metallic ferrule cup l5, the circle defined by the interior surfaces of the indentations Will not be greater in diameter than the outside diameter of the tube i(l.

The elasticity of the metal of the ferrule cup l5, tending to restore the cup to its initial undistorted position will corripehsate for the expansion of the material. Where distortion has been mentioned in the foregoing, it does not mean that the ferrule cup is twisted or misshapen when mounted on the unit. The distortion referred to is only the initial give or very slight change in the diameter of the cylindrical wall 20 when the metallic ferrule cup I5 is forced over the end of the tube IO. Since the ceramic tube o has substantially no expansion at all under heat treating processes and the material of the metallic ferrule cup 'l5 may have a substantial coefficient of expansion, the difierene between the coefiicients of expansion is relatively large. However, the absolute amount of expansion of the metallic ferrule cup l5, while it is sufiicient to loosen the metallic ferrule cup when it is expanded by heat, is nevertheless very small, and the iridentations 30 which are provided co1hpensate for this expansion. The distortion of the wall 0 of the ferrule l5 When it is placed over the end of the tube IO is very small, is not visible to the eye, and does not affect the usef-ul dimension thereof.

It will be obvious that the indentations 3D, instead of being part s'pherical, as shown in Figure 1, may have any appropriate shape which will accomplish the same purpose. Thus, as shown in Figure 3, the indentations 30 may be longitudinal rectangular indentations where the wall of the indentation defines a portion of a cylinder. As shown in Figure 4, the indentation 239 may be in the form of two intersecting substantially rectangular indentations which will afford an even better grip. Other forms of indentations may be used.

All of the foregoing holding means which are integral with th ferrule cup l5 and which may be used separately or in combination have as their common function, the definng of a circle by their interior surfaces, the circumference of which circle is less than the outer diameter of the tube il so that the material in the ferrule cup i5 will be elastically distorted to a slight extent when the ferrule cup l5 is forced over the end of the tube IO. This will create an elastic force tending to compress the wall of the ferrule 15, which elastc compressive force will compensate for and counteract the expansion of the material of the metallic ferrule cup |5 When the entire unit is subjected to baking, firing or other heat treating processes.

In Figures 5 and -2, we have shown a slight modification of our ferrule which will simplify the connection between the resistance wire and the ferrule. In these figures, the flange 2| of the ferrule l5' has no slits for wire fastening. In stead, a very thin (of the order of 38 gauge) strip 40 of copper having a reentrant flange dl and notches 42 in its end 43 is used. The strip 45 is placed on the end of the tube IO so that fiange 4| bears against end H of tube IO and the body of the strip bears against the side of the tube. The ferrule l5 is forced on holding the strip 40 in place and making electrical contact therewith. The resistance wire may now be wound around notches 42 in end 43 of the strip 40.

It will be obvious therefore that our invention may be embodied in many modifications and variations"which should now be obvious to those skilled in the art. Accordingly, therefore, we prefer to be bound not by the specific disclosures her-ein, but only by the appended claim.

We claim:

In combination, a ferrule and a resistor, said resistor having a ceramic tube, said ferrule being arranged to fit over the end of said tube; said ferrule having a cylindrical wall of a diameter slightly less than the Outer diameter of said tube;

said Wall having indentations, said indentations forming convex areas on the interior wall of said cyiindrical wall, the circle defined by the interior surfaces of said indentations being of slighcly less circumference than the outer diameter of said tube; said ferrule being made of eictrically conductive eiastic material sufiicient to permit said ferrule to be forced over and be gripped by the end of said tube and sufficient so that irrespective of the amount of expansion which normally occurs to said metallic ferrule, the circle defined by the interior surface of said indentations will not be greater than the outside diameter of said tube; and a conductive strip; said strip being held in position by said ferruie; said strip comprising means for effecting a conductive connection to a wire.

WILLIAM ALLEVA.

HERBERT BLACKBURN.

REFERENCES CITED The following references are of record in the 5 file of this patent:

UNITED STATES PATENIS 

